Must vs. Have to

Use 'have to' in the past, present and future to express responsibility or necessity. NOTE: 'have to' is conjugated as a regular verb and therefore requires an auxiliary verb in the question form or negative.

Examples:

I have to arrive at work at 9 sharp. My boss is very strict.

We have to give him our answer today or lose out on the contract.

You have to pass your exams or the university will not accept you.

I have to send a report to Head Office every week.

Must do - Obligations

Use 'must' to express something that you or a person feels is necessary. This form is used only in the present and future.

Examples:

I must go to bed earlier.

They must do something about it.

You must come and see us some time.

I must say, I don't think you were very nice to him.

Don't have to do - Not Required

The negative form of 'have to' expresses the idea that something is not required. It is however, possible if so desired.

Examples:

I don't have to listen to this. I'm leaving.

You don't have to come if you don't want to.

Mustn't do - Prohibition

The negative form of 'must' expresses the idea that something is prohibited - this form is very different in meaning than the negative of 'have to'!